Urechis

Urechis
	Urechis unicinctus as food
Systematics
Trunk :	Annelids (Annelida)
Class :	Hedgehog worms (Echiura)
Order :	Echiuroidea
Subordination :	Echiurida
Family :	Urechidae
Genre :	Urechis
Scientific name of the family
	Urechidae
	Monro , 1927
Scientific name of the genus
	Urechis
	Seitz , 1907

Urechis is the name of a genus of large, in the sand burrowing hedgehog worms (Echiura), which at the same time forms the monogeneric family of Urechidae andincludesfour species in the Pacific Ocean .

features

The hedgehog worms of the genus Urechis or family Urechidae are large to very large with body lengths of up to 50 cm (in the North American species Urechis caupo ). The trunk is sausage-shaped with a wrinkled skin and a short, spoon-shaped proboscis . There are two hooks on the front of the trunk on the abdomen and a ring with anal bristles around the anus at the end of the trunk. Next to the kidney exits on the front part of the trunk, mucous glands open outwards.

The animals have 2 or 3 pairs of nephridia , in which the lips of the nephrostomata are always spirally wound. At the end of the intestine are two long anal vesicles. The rear section of the midgut is greatly expanded and serves as a respiratory organ, with the respiratory water flowing in and out through the anus. In contrast to all other known hedgehog worms, no blood vessels are formed. Most authors speak of an open blood vessel system, in which the blood corresponds to the fluid in the coelom . In addition to numerous amebocytes , the blood also contains many semicircular red blood cells about 25 µm in size with hemoglobin , which store oxygen and enable survival in an oxygen-poor environment.

The longitudinal muscles of the cutaneous muscle tube sit between the outer ring muscles and the inner transverse muscles.

Life cycle

Males and females are the same size for all Urechis species. Fertilization is external and development is via a swimming trochophora larva.

Way of life

All Urechis species dig their U-shaped tunnels in the soft ground (sand, mud) themselves. Peristaltic movements of the body create a water flow in the tunnels, through which dissolved oxygen and food particles are swirled around. Like other hedgehog worms, the urchis feed on detritus and microorganisms, but do not have a long proboscis to absorb them from the substrate. Instead, they use their mucous glands to produce a mucous network with which the food particles are filtered out of the seawater . If the slime web is full, it is consumed with the adhering particles.

species

There are four known Urechis species:

Urechis caupo Fisher & MacGinitie, 1928 on the North American Pacific coast,
Urechis chilensis (M. Müller, 1852) on the southern coast of Chile ,
Urechis novaezealandiae (Dendy, 1898) on the coasts of New Zealand ,
Urechis unicinctus (Drasche, 1880) on the coasts of Japan , Korea and China .

The four Urechis species cannot be distinguished based on their external characteristics. However, since their areas of distribution do not overlap, the place of origin is a reliable identifier (as long as there are no carryovers). The most important internal distinguishing feature is the number of nephridia: While Urechis chilensis and Urechis caupo have 3 pairs of nephridia, Urechis unicinctus and Urechis novaezealandiae only have 2 pairs. In Urechis caupo , unlike Urechis chilensis, under the microscope you can see that the two front hooks on the abdomen are sharply pointed. Urechis novaezealandiae , which also has sharply pointed front hooks, is much larger in size than Urechis unicinctus . In Urechis novaezealandiae , in which the esophagus, stomach and the intestinal section behind the respiratory organ are very long, there may occasionally be another unpaired (fifth) nephridium in addition to the two pairs of nephridia.

Local trivial names and meanings for humans

Urechis unicinctus is eaten in China, Korea, and Japan. Because of its resemblance to a human penis , it is also referred to there as the "penis fish" (陰莖魚). In the USA, Urechis caupo is also known as the fat innkeeper worm , as its cave is inhabited by numerous commensals .

Web links

Commons : Urechis - collection of images, videos and audio files

Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Phylum Echiura. P. 24f., Family Urechidae.

Individual evidence

^ William Wallace Newby: The embryology of the echiuroid worm, Urechis caupo. The American Philosophical Society, 1940, p. 144.
^ Alfred C. Redfield, Marcel Florkin (1931): The Respiratory Function of the Blood of Urechis Caupo. Biological Bulletin 61 (2), pp. 185-210.
^ H. Sato (1939): Studies on the Echiuroidea, Sipunculoidea and Priapuloidea of Japan. Science Reports of the Tôhoku University, Ser. 4 (Biology), Volume 14, pp. 339-460, here p. 350.
↑ WK Fisher, GE MacGinitie, 1928: The natural history of an echiuroid worm (Urechis). Ann. Mag. Natural History (10) 1, pp. 204-213.
^ GA Knox, 1957 Urechis novaezealandiae (Dendy): a New Zealand echiuroid. Transactions of The Royal Society of New Zealand 85, pp. 141-148 ( PDF ).

[1] William Wallace Newby: The embryology of the echiuroid worm, Urechis caupo. The American Philosophical Society, 1940, p. 144.

[2] Alfred C. Redfield, Marcel Florkin (1931): The Respiratory Function of the Blood of Urechis Caupo. Biological Bulletin 61 (2), pp. 185-210.

[3] H. Sato (1939): Studies on the Echiuroidea, Sipunculoidea and Priapuloidea of Japan. Science Reports of the Tôhoku University, Ser. 4 (Biology), Volume 14, pp. 339-460, here p. 350.

[4] WK Fisher, GE MacGinitie, 1928: The natural history of an echiuroid worm (Urechis). Ann. Mag. Natural History (10) 1, pp. 204-213.

[5] GA Knox, 1957 Urechis novaezealandiae (Dendy): a New Zealand echiuroid. Transactions of The Royal Society of New Zealand 85, pp. 141-148 ( PDF ).